Campbell, SJ, Simmons, RW & Rickson, RJ 2013, 'Differences in the erodibility and hydrological response of slope forming materials from an iron ore mine, West Africa', in M Tibbett, AB Fourie & C Digby (eds), Proceedings of the Eighth International Seminar on Mine Closure
, Australian Centre for Geomechanics, Cornwall, pp. 239-250, https://doi.org/10.36487/ACG_rep/1352_20_Simmons
Published data are sparse on the erodibility and hydrological response of slope-forming materials (SFMs) commonly found at iron ore mine sites, such as ore, soil and waste rock. This research critically evaluates the erodibility and hydrological response of 10 SFMs derived from an iron ore mine in West Africa. The SFMs were tested under both field-capacity and air-dry antecedent moisture conditions, indicative of soil moisture status both before and during the onset of monsoonal rains. The total volumes of runoff and of leachate generated by each of the SFMs when subjected to simulated rainfall were determined. The sediment load (TSL) of the runoff and leachate were also measured. Three replicates of each SFM at each antecedent moisture condition were prepared in 0.5 × 0.25 × 0.15 m erosion trays set on a 10 degree gradient. Each replicate was subjected to a design-storm of 100 mm hrˉ¹ for 30 minutes duration. Statistical differences in the measured erodibility (material eroded) and hydrological response were evaluated using One-way ANOVA with Post-hoc Fisher LSD, using STATISTICA software. Further, multiple-regression analysis (MRA) was used to correlate the physical and chemical properties of the SFMs with their erodibility and hydrological response under the design storm event. Properties included in the MRA were organic carbon, cation exchange capacity, pH, EC, density, particle size and dry-aggregate distribution, mineralogy and magnetic susceptibility. The weathered phyllite (PHY-WEA) waste-rock and colluvial soil (SRE) gave significantly higher runoff volumes when compared with all other SFMs. In contrast, with the exception of PHY-WEA and SRE, at both antecedent moisture conditions, all other SFMs gave significantly higher leachate as compared with runoff volumes. PHY-WEA also produced significantly higher TSL when compared with all other treatments, with mean values of 47.8 g and 165 g per erosion tray, respectively. This equates to TSC concentrations of 14.3 and 26.2 g l-1, which are well in excess of the mine water quality target of < 0.05 g l-1. The results of this research provide a greater understanding of the erodibility and hydrological response of ore, soil and waste rock SFMs. The research findings have important implications for the management and design of ore stock piles, waste rock dumps, sedimentation ponds and water discharge structures at mine sites. The MRA results demonstrate that variables including magnetic susceptibility, bulk mineralogy and dry aggregate distribution, which are not commonly assessed in erosion studies, are important parameters governing the erodibility and hydrological response of SFMs.
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